Magnetron with an improved tuning mechanism

ABSTRACT

A magnetron wherein tuning of the frequency is produced by penetration of conductive cores into its cavities. Said cores are fixed on a bearer and the magnetron comprises means for translating the bearer along its axis and simultaneously maintaining the vacuum in the tube, there means being designed for biasing said bearer at three points distributed in the neighbourhood of its periphery.

United States Patent [19 Peyrard et al.

[111 3,870,923 1 1 Mar. 11, 1975 MAGNETRON WITH AN IMPROVED TUNING MECHANISM [75] Inventors: Yves Peyrard; Jean-Claude Renault,

both of Paris, France [73] Assignee: Thomson-CSF, Paris, France [22] Filed: Dec. 26, 1973 [21] Appl. No.: 427,500

[30] Foreign Application Priority Data Dec. 29, 1972 France 72.46905 [52] U.S. Cl 315/3955, 315/3951, 315/3961 [51] Int. Cl. H0lj 25/50 [58] Field of Search 313/337, 338; 315/3951,

[56] References Cited UNITED STATES PATENTS 12/1950 Donal, Jr. et a1 315/3957 1/1953 2,632,131 3/1953 La Rue.. 315/3961 2,851,633 9/1958 Dubois 315/3955 X 3,414,761 12/1968 Glenficld 315/3961 3,590,313 6/1971 Stoke 315/3977 Primary ExaminerAlfred E. Smith Assistant ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or Firm-Roland Plottel, Esq.

[57] ABSTRACT A magnetron wherein tuning of the frequency is produced by penetration of conductive cores into its cavities. Said cores are fixed on a bearer and the magnetron comprises means for translating the bearer along its axis and simultaneously maintaining the vacuum in the tube, there'means being designed for biasing said bearer at three points distributed in the neighbourhood of itsperiphery.

4 Claims, 2 Drawing Figures PATENTED 1 I975 3.870.923

ll lmw llll 1mm um MAGNETRON WITH AN IMPROVED TUNING MECHANISM The present invention relates to magnetrons. It relates more particularly to, the mechanism for tuning the frequency of these electronic tubes.

These tubes generally comprise, arranged around an axis and within a cylindrical body, a plurality of electromagnetic cavities, that is to say volumes which are limited on some of their faces by conductive walls, and in which, in operation, a high frequency electromagnetic field is developed. An electron beam issuing from a source located at the centre of the cylindrical body is accelerated towards said cavities, whilst a magnetic field is developed in the direction of the cylinder axis. Finally, in certain of these tubes, arrangements are effected in order to make it possible to vary the resonance frequencies of the electromagnetic cavities. The cylindrical body is closed off at its two ends by two faces, perpendicular to the axis of the body, and attached to the latter in a vacuum-tight fashion, a vacuum being maintained within the closed envelope thus constituted.

Questions of size arise on the one hand in positioning the tube itself between the poles of the magnet, generally a permanent magnet, which produces the magnetic field required for the operation of the tube, and on the other hand in positioning the components of the tuning mechanism.

In some magnetrons, tuning of the frequency is achieved by displacement of electrically conductive cores, or plungers, which are able to penetrate to a greater or lesser extent into the afore mentioned electromagnetic cavities, thus modifying the resonance frequencies of the cavities. It goes without saying that the displacement should be effected without any breaking of the vacuum.

In the prior art, the displacement of the plungers was separately realized for each of the cavities, or by the displacement of one of the terminal face of the magnetron, to which were attached the plungers; in this latter embodiment, the method required to produce this displacement was usually applied to the centre of the face and this gave rise to major complications in the installation of the deforming system, due to the presence in this region of the magnet poles. Moreover, as experience has shown, the displacements of all the plungers were not exactly the same and, consequently, the degrees of penetration of the cores into the cavities were not equal too, so that resonance frequencies differed from one cavity to another.

The object of the present invention is a tunable magnetron in which these difficulties are avoided. In accordance with the present invention, there is provided a magnetron comprising:

a cylindrical body;

N cavities with electrically conductive walls formed in said body;

two covers, closing off the ends of said body in a neighbourhood of its periphery, said cores thus penetrating into said cavities through a height depending upon the translational movement of said bearer,

and sealing means for maintaining the vacuum in the enclosure duringsaid translational movement.

FIG. 1 is a perspective view of a portion of a magnetron illustrating the invention generally.

FIG. 2 is a partial cross-sectional view taken along lines II of FIG. 1, and showing additional parts of the magnetron not shown in FIG. 1. It illustrates an embodiment of the invention in detail.

FIG. 1 illustrates in perspective one of the faces or covers 1 which close off the cylindrical body of the magnetron comprising the resonant cavities, said body not having been described or illustrated in the present text anymore than have those other elements of the magnetron which are not directly concerned in the invention. Said body, in the figure, would be located beneath the component shown in the figure. We will confine ourselves here to a reminder that in one of its most usual forms, it consists of a cylindrical electrically conductive wall equipped around the whole of its circumference with partitions or fins, also electrically conductive, disposed radially and extending towards the interior of the cylinder, up to a certain distance from its centre. These partitions delimit the pluralilty of resonant cavities referred to, for example N cavities, which are open at three of their faces: that disposed towards the cylinder axis and those perpendicular to said axis. The cylindrical body in which, in operation, there is a vacuum, is closed off at its other end by a flat base. In the figure, XX is the axis of the cover 1, and is coincident with that of the magnetron of which it forms part.

The cover 1 is constituted by a circular flange 2 with double stepped portions, 3 and 4, at one side, and also stepped, at 5, at the other side. The flange 2 carries an assembly 6 constituted by a bearer 7, disc shapped, of the same diameter as the step or shoulder 5 in the example shown in the figure, to which are attached electrically conductive cores 8, for example N cores. The flange 2 is attached to the assembly 6 in a manner which will be specified hereinafter. Three toothed wheels 17 are also shown on the figure, and are described hereinafter too.

Among the components numerated hereinbefore, certain of them, at least at the surface, should exhibit high electrical conductivity for satisfactory operation of the magnetron, as in prior art electronic tubes of this kind, whilst others should have a high mechanical strength in view of the forces they have to withstand when the tuning mechanism is operated. These conditions have a bearing upon the design of the component shown FIG. 1. An example of this design is given hereinafter.

The flange 2 of anti-magnetic steel and the cylindrical ring 5, are manufactured separately. Said ring 5 is attached to the flange 2 by brazing, using a silver brazing solder. To a disc 7, machined in anti-magnetic steel, on the other hand a copper ring corresponding to the height of the cores 8, is attached; said ring is brazed to the disc 7 using a silver brazing solder for example. Then, the copper ring is milled in order to produce the cores 8, all having the same dimension in the particular example shown in the FIG. 1.

The assembly 6, thus constituted by the bearer 7 and the cores 8, is attached to the cover 1 at three points.

FIG. 2 illustrates in partial section on the axis II, one of the possible embodiments of this attachment. This figure also shows, likewise in section, the components of the tuning mechanism. In this figure, all components which occur in FIG. I, carry the same references which they have there. In the embodiment shown in FIG. 2, the flange 2 is recessed at its centre, as the drawing shows, whilst the bearer 7, reduced to a disc in the case of FIG. 1, extends this time in the form of a dished portion 70 whose function will be evident later on. The brazed joints referred to hereinbefore, are marked by 50 and 80 in the section view of the FIG. 2.

The flange 2 is brazed at 20 to the cylindrical body of the magnetron marked by 100.

A sub-assembly is produced separately; it is constituted by a deformable diaphragm of generally tubular shape, for example a bellows l terminated by a dished end cover.9 brazed to it at its bottom end and by a flanged ring 11 brazed to the top end of the bellows. The brazed joints of this assembly, produced using a known technique, have not been shown simply in order to avoid over-burdening the drawing. This subassembly is installed between the cover 1 and the bearer 7 as the figure shows, the dished ring 9 resting on the assembly 6 and the ring 11 on the flange 2. The dished ring 9, at its centre exhibits a hollow cylindrical body 12, either attached to it or formed integrally with it, which, in the position shown in the drawing, penetrates into a cavity in the core 8 and is flush with the bottom end of the latter. Sub-assembly 9, 10, 11 and 12, is brazed at its two ends on the one hand to the assembly 6 and on the other hand to the flange 2, respectively at 13 and 14.

The hollow cylindrical body 12 is provided internally with a blind tapped hole 15, thus constituting a nut, into which there can be screwed a screw 16 terminated in a head 17 having the form of a toothed wheel and forming a gear in other words, the bearer 7 which carries all the cores 8, is driven on three points by the ball bearing 18; the top face of thetoothed wheel 17 is flush with a level located slightly below the lowest point of the step 4. A rim 19, attached to the flange 2,

' screwed in position for example (screws not visible in the figure), limits the upward displacements of the toothed wheel 17. An intermediate ring 21, with double toothing, held between the flange 2 around the stepped portion 3 (FIG. 1), and the rim 19 by the bearings 22 and 23, meshes with the gear 17. An other gear 24 controls the rotation of the intermediate ring 21. The spindle of this control gear has been marked 25. Rotation of the control gear 24 is produced either manually or by a low-speed motor (not shown), assembled on the spindle at 26. The references 27 and 28 represent the frame, fixed by some suitable prior art technique, to the body 100 of the tube, and 29 a housing atached to the frame by the screw 30.

The execution of the various brazing operations which are referred to hereinbefore, as well as the order in which these operations should be carried out so that they do not interfere with one another (i.e., so that the 6 tubes. For this reason, this point will not be dealt with here nor for that matter .will be choise of the various materials utilised, especially in terms of their magnetic properties, aspects which are likewise within the scope of the person skilled in the art.

It should be pointed out, however, that in the embodiment shown in FIG. 2, the cores do not have the constant height exhibited by those of FIG. I; this detail is without importance as far as the invention is con cerned.

The rotation of the control gear 24 causes the intermediate ring 21 to rotate, and this, in turn, rotates the gears 17 so that the cores 8 move up or down depending upon the direction of rotation. This displacement is made possible, without breaking the vacuum, by the presence of the deformable bellows 10 which provides a vacuum-tight seal vis-a-vis the exterior.

The cores 8 thus penetrate to a greater or lesser depth into the cavities contained by the cylindrical body 100. With each position of these cores or plungers 8, there corresponds a resonance frequency on the part of these cavities. In the figure, reference 32 represents one of the aforementioned fins, separating two successive cavities of the magnetron, and reference 31, in section, represents the coupling element between them. The amplitude of the maximum possible displacement is limited by the distance 33 (shown FIG. 1) between the component 5 and the highest point of the ring 6 (bearer 7). This displacement is at the most some few millimetres for a magnetron operating at a wavelength of 10 cm.

In the magnetrons in accordance with the invention, the cover 1 carries the three toothed wheels 17, contained in the same plane as FIG. 1 shows. These toothed wheels will preferentially, as in the example of this figure, be arranged at 120 to one another. Thanks to the presence of these three wheels, the bearer 7 and its cores 8, in the course of its displacement, is biased simultaneously by three points distributed uniformly about its axis so that it displaces very substantially along the direction of said axis. Thus, one of the drawbacks of the prior art devices is avoided.

Finally, in particular on FIG. 2, it will be observed that in the magnetrons in accordance with the invention there is no part of the tuning mechanism located in the region of the axis of the tube disposed to the left beyond the limits of the figure; this region is left free for the installation of the magnet outside the tube, thus overcoming the other drawback referred to earlier.

In the embodiment of the invention, shown in FIG. 2, the bearer 7 shown in FIG. 1 is integral with a thick metal diaphragm which is rigid and dished to give it a dome shape in the example illustrated, there being a central hole in it which is not visible in the figure. The components 7 and 70 are also made in one piece by stamping a flange. The presence of this diaphragm increases the stiffness of the ring 6 and thus reduces the risk of the latter displacing in a direction out of alignment with the tube axis.

Of course, the invention is not limited to the embodiment described and shown which was given solely by way of example.

What is claimed is:

l. A magnetron comprising:

a cylindrical body;

N cavities with electrically conductive walls formed in said body;

two covers, closing off the ends of said body in a vacuum-tight fashion, thus delimiting an enclosure which is maintained under vacuum in operation;

at least N electrically conductive tuning cores, said tuning cores being attached to a bearer, said bearer being carried by one of said covers;

means for translating said bearer in a direction substantially parallel to the axis of said body, simultaneously on three points distributed substantially at the periphery of said bearer, said tuning cores thus penetrating into said cavities through a height depending upon the magnitude of the translation of said bearer;

and sealing means for maintaining the vacuum in the enclosure during said translation.

2. A magnetron as claimed in claim 1, wherein said translational means comprise three screws fixed in the axial direction in relation to said cover and cooperating with three nuts carried by said bearer.

3. A magnetron as claimed in claim 2, wherein said sealing means consist of three deformable diaphragms of generally tubular shape, surrounding each of said three screws and attached at one of their ends to said bearer and at the other to said cover.

4. A magnetron as claimed in claim 2, wherein said three screws carry three gears meshing with an intermediate toothed ring rotated by a control gear assembled on said cylindrical body and operated by a control spindle. 

1. A magnetron comprising: a cylindrical body; N cavities with electrically conductive walls formed in said body; two covers, closing off the ends of said body in a vacuum-tight fashion, thus delimiting an enclosure which is maintained under vacuum in operation; at least N electrically conductive tuning cores, said tuning cores being attached to a bearer, said bearer being carried by one of said covers; means for translating said bearer in a direction substantially parallel to the axis of said body, simultaneously on three points distributed substantially at the periphery of said bearer, said tuning cores thus penetrating into said cavities through a height depending upon the magnitude of the translation of said bearer; and sealing means for maintaining the vacuum in the enclosure during said translation.
 1. A magnetron comprising: a cylindrical body; N cavities with electrically conductive walls formed in said body; two covers, closing off the ends of said body in a vacuum-tight fashion, thus delimiting an enclosure which is maintained under vacuum in operation; at least N electrically conductive tuning cores, said tuning cores being attached to a bearer, said bearer being carried by one of said covers; means for translating said bearer in a direction substantially parallel to the axis of said body, simultaneously on three points distributed substantially at the periphery of said bearer, said tuning cores thus penetrating into said cavities through a height depending upon the magnitude of the translation of said bearer; and sealing means for maintaining the vacuum in the enclosure during said translation.
 2. A magnetron as claimed in claim 1, wherein said translational means comprise three screws fixed in the axial direction in relation to said cover and cooperating with three nuts carried by said bearer.
 3. A magnetron as claimed in claim 2, wherein said sealing means consist of three deformable diaphragms of generally tubular shape, surrounding each of said three screws and attached at one of their ends to said bearer and at the other to said cover. 